Microstructural optimization of LaMg12 alloy for hydrogen storage
Microstructural optimization of LaMg12 alloy for hydrogen storage
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DOI：
10.1016/j.jallcom.2010.09.172
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发表时间：
2011-09
影响因子：
6.2
通讯作者：
A. Poletaev;R. Denys;J. K. Solberg;B. Tarasov;V. Yartys
中科院分区：
文献类型：
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作者：
A. Poletaev;R. Denys;J. K. Solberg;B. Tarasov;V. Yartys
将快速凝固技术应用于 LaMg12 合金，以实现晶粒尺寸的细化。通过在氩气氛中使用三种不同的旋转速度（3.1、10.5 和 20.9m/s）在旋转铜轮上固化熔体来生产薄带。通过同步加速器 X 射线衍射 (SR XRD)、电子探针微量分析 (EPMA) 和 TEM 对带材进行了分析，并对它们进行了氢吸收-解吸循环和热解吸光谱 (TDS) 表征。 SR XRD 和 EPMA 显示形成了两相：LaMg12−x 和 Mg。从SR XRD发现，根据冷却速率，LaMg12−x合金会结晶出三种不同的结构变化：六方TbCu7（最高冷却速率）、四方ThMn12（中等冷却速率）和斜方晶系LaMg11型（最低冷却速率）。亚稳态 TbCu7 型结构（sp. gr. P6/mmm；a=5.9617(3)；c=5.2153(5)Å）在早期的研究中尚不清楚，这是首次报道 La-Mg 体系。通过扫描电子显微镜 (SEM) 研究发现，RS 会导致显着的晶粒细化和非晶化，从而实现最高的冷却速率。形成的氢化物相的颗粒尺寸在 0.2–3μm 范围内变化，具体取决于用于制备原始合金的 RS 合成路线。吸氢导致两步歧化过程：LaMg12+H2→LaH3+Mg→LaH3+MgH2。晶粒尺寸的减小改善了氢化动力学。通过 TDS 和原位 SR XRD 研究的氢解吸显示，在~370°C 处有一个析氢主峰。对于以 10.5m/s 和 20.9m/s 合成的合金，伴随着 415°C 的额外解吸事件。这个额外的峰与 450°C 以下的 LaH2 中的 Mg 辅助低温氢解吸有关，并导致复合过程形成初始金属间合金 LaMg12。
A Rapid Solidification technique was applied to a LaMg12alloy in order to achieve refinement of the grain size. Thin ribbons were produced by solidifying the melt on a spinning copper wheel in an argon atmosphere using three different rotations speeds, 3.1, 10.5 and 20.9m/s. The ribbons were analyzed by synchrotron X-ray diffraction (SR XRD), electron probe microanalysis (EPMA), and TEM, and they were subjected to hydrogen absorption–desorption cycling and to thermal desorption spectroscopy (TDS) characterization. SR XRD and EPMA revealed formation of two phases, LaMg12−xand Mg. From SR XRD it was found that, depending on the cooling rate, the LaMg12−xalloy crystallized with three different structural modifications, hexagonal TbCu7(highest cooling rate), tetragonal ThMn12(medium cooling rate) and orthorhombic LaMg11type (lowest cooling rate). A metastable TbCu7-type structure (sp. gr. P6/mmm; a=5.9617(3); c=5.2153(5)Å) was not known from the earlier performed research and is reported for the La–Mg system for the first time. From the scanning electron microscopy (SEM) studies, RS was found to cause a significant grain refinement and an amorphisation for the highest cooling rate. The particle size of the formed hydride phases varied in the range 0.2–3μm depending on the RS synthesis route used to prepare the original alloy. Hydrogen absorption resulted in a two-step disproportionation process: LaMg12+H2→LaH3+Mg→LaH3+MgH2. A decrease in the grain size improved the hydrogenation kinetics. Hydrogen desorption studied by TDS and in situ SR XRD showed a major peak of hydrogen evolution at ∼370°C. For the alloys synthesized at 10.5m/s and 20.9m/s, it was accompanied by an extra desorption event at 415°C. This extra peak was associated with Mg-assisted low temperature hydrogen desorption from LaH2proceeding below 450°C and leading to a recombination process to form the initial intermetallic alloy LaMg12.